Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$236.92	5.225%	$249.2991	$249.30	$249.30	$249.30
Purchase #2	$125.33	9.183%	$136.8391	$136.84	$136.85	$136.80
Purchase #3	$85.49	7.454%	$91.8624	$91.86	$91.85	$91.90
Purchase #4	$192.54	4.180%	$200.5882	$200.59	$200.60	$200.60
Purchase #5	$111.82	13.222%	$126.6048	$126.60	$126.60	$126.60
Purchase #6	$14.33	3.844%	$14.8808	$14.88	$14.90	$14.90
Purchase #7	$91.78	8.765%	$99.8245	$99.82	$99.80	$99.80
7 purchase totals =	$858.21		$919.8989	$919.89	$919.90	$919.90